Verify that severe circadian rhythm phase abnormalities occur frequently among volunteers ages 60+ years by measuring circadian rhythms in salivary and blood melatonin as well as the urinary 6-sulphatoxy metabolite, supplemented by measures of urinary cortisol and core temperature in an aging sample selected for likely circadian deviation. Correlate rhythm phases among these circadian rhythms. Determine and re-test longitudinal stability of circadian rhythm abnormalities, test the light-responsiveness of the photic light-measurement pathways by determining melatonin suppression during exposure to moderate light, measure circadian rhythms and light responsiveness in healthy adults ages 20-40 years to expand control data for contrast with volunteers ages 60+, explore whether abnormal light exposure, habits or patterns of medication use could acount for observed circadian abnormalities.